Axial Stress-Strain Response of HDPE from Whole Pipes and Coupons

Abstract

High-density polyethylene (HDPE) pipes are subjected to tensile stresses and strains in the axial direction during and after a pulled-in-place installation by horizontal directional drilling or pipe bursting. During these types of installation techniques, creep and stress relaxation are prevalent conditions acting on the pipe. Results from stress relaxation and creep experiments conducted on both whole HDPE pipe samples and coupons trimmed from a pipe’s wall are reported. Stress relaxation experiments were performed at axial strain levels of 3, 1, and 0.5%, and creep experiments were performed at stress levels of 8 and 4 MPa. The merit of testing whole pipe samples as opposed to simply testing coupons trimmed from the pipe wall is investigated by comparing the responses of the pipe samples and coupons. For the particular conditions tested, it was shown that coupons trimmed from the barrel of a pipe responded differently than the whole pipe barrel. In fact, the coupons appeared to exhibit a higher modulus than the whole pipe samples. However, the benefit of testing whole pipe samples is overshadowed by the relative ease with which experiments on coupons can be conducted.